Difference between OS and DATABLOCK images?


one of the things which make OpenNebula usage overly complicated is the fact that I cannot create an empty image of type OS. Only DATABLOCK can be created this way, and it can be changed to OS afterwards.

Is there any further difference between these two types of images? So far they both look similar to me, with creation of an empty image being the only difference.

If they are indeed so similar, can the abovementioned limitation of type OS (creating an empty image) be removed?



I think one of the main differences between an OS and a DATABLOCK image is that a VM requires at least an OS image to boot from. Maybe I’m wrong but you can’t boot a VM from a DATABLOCK image, you can use it to install an OS on it though.


Each VM need at least one OS type image so that the system knows which disk to boot from. Other than this, they are both same.

This is probably not true - I have several VMs in my ONe that have only disks of type DATABLOCK and CONTEXT, and they work without problem.

Maybe the default boot order is set based on the image type? But even then, a VM can have multiple images of type OS.

Yes. When setting the automatic device targets the OS disk(s) are moved to the head of the ordering queue.

There is a ticket already to rethink this OS-datablock differences, #4740